Signaling system



Patented Sept. 9, 1924.

UNITED [STATES PAlEN-T "OFFICE.

CHARLES A. ROBINSON, WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR. TO-

WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPOBA v TION or YORK.

SIGNALING srs'rma application filed December 17, 1921. Serial No. 523,018.

To all whom it 'may cmzcem:

Be it'known that I, Crmnnss A. Ronmsou,

a citizen of the United States, residing at Washington, in the District of Columbia, haveinvented certain new and useful Improvements inSignaling Systems, of which thefollowing is a full, clear, concise, and exact description.

This invention relates to signaling systemsin which it is desired to transmit cur-- rents of different 'fr uencies at different times as, for instance, 1; 1e talking and rings m frequencies in a telephone circuit. The ob ect of the invention is to make the circuit efficient for transmitting currents ofeither frequency range.

the particular range of frequencies which it is expected to. employ, and a circuit so designedis relatively inefficient for transmitting other frequencies. One case in whichthis inefiiciency becomes a serious difiiculty is in connection with repeaters such as vacu;

' um tube repeaters used in a telephone trans mission line. The transformers or inductances used throughout the ci cuit and particularly in theimmediate input and output circuits of the repeaterare such as to transmit. telephone frequencies with good efiiciency but currents are so discriminatcd' a ainst t at in spite of'amphjication by t e repeater they may not be able to operate the ringers at the terminal of the line. This difliculty has been overcome in part by changing the character of the input circuit during ringing, as for example, by making the inputclrcuit anti-,

resonant for rin 'ng frequency. This may be accomplished y suitably operated relays 'as will be described later, these relays being 0 ated by the output ringing current. I fin however that in some cases thls amplified ringing current is not large enough to operate the relays with certainty. My' invention resides in further increasing the -effieiency and certainty for. ringing freuencies and in brief, consists in increasing t a gain of the repeater, thereby increasing the output of ringing current to a value which will operate the relay with certainty. This, however, will also increase the gain for the telephone currents and raise it to a by means of the. transform r 16. strength of the input impulses impresed on transmission level in excess of that intended 'forthat portion of the line. Accordingly in my invention I provide means to attenuate the output of the repeater in. a manner which does not affect the operation of the relays. i

The invention will be better understood by reference to the accompanying drawings, in which Fig. 1 shows a circuit embodying my invention. Fig. 2. is a modification thereof, showing certain disposition of impedance elements to obtain the desircd re sults. Figs. 3 5 and 7 show specific arrangements for obtainirig the desired results, and Figs. 4 and Gare curves illustrating the operation for the circuits-of Fifa3and5. 1 i

n Fi .1, 11 represents an incoming transmission ine over which may be transmitted both telephone currents and rin ng currents. A vacuum tube repeater e ement 12 has its input associated with the line 11 by means'ofa transformer 14, its output being associated with the outgoing line 15 The the repeater element may be controlled'by a potentiometer 17 in a well-nnown manner.

ower for the repeater element is supplied by a battery 18 connected from filament to plate andincluding in its circuit aretard coil 19. The very'low efficiency of the circuit for ringing frequencies; due to the de-, sign'of the transformers 14 and 16, has part been overcome by the introduction ofa relay 20 through which the alternating current component of the output of the amplifier of ringing frequency may ass. The condensers 21 and 22 are insertefas shown to prevent the discharge of the battery 18 through the output of the repeater elementand to offer a path of low impedance for high frequencies around the relay, 20. The relay 20 through its contact 23 controls a second relay 24. Through its front contact the relay 211, which is normally actuated, connectsthe potentiometer 17 across the primary of the transformer 14. Through its back contact this relay upon release, bridges a condenser. 27 across the primary of the transformer 14 and the potentiometer 17 is cut out by the opening of the front con tact. The capacity ofthecondenser 27 is so chosen that with the primary of the re eater as a; whole for ringing frequencies.

'e circuit as thus-iar iescribed is'substantially that now coinmonlynsedinpracates in the same manner. However, there is shunted around the front contact, resistance element 28 so that the condenser 27 at all times is bridged around the primary of -ticc,but it is found that in the caseoffesei:ies'with this condenser 27, the resistance peaters'working at a low energy level there is considerable uncertainty as to the opera- Y. ringing current in the output'of there'peater tionoi the relay 20 forthe reason that the may be too small. :To increase the certainty of operations, I increase the gain of the repeater by adjusting the. potentiometer 17 tosuch a point: that the amplified ringing current can be-relied on to; operate relay 20 without fail, Itis desirable; however, that the telephone current transmitted :0verithe line 15 shall have" acertain 'amplitud the gain the to .the newladjustme potentiometer shouldbe coinpensa ed -t n some manner. This latter, complish by means of a network Z, whichnwi llact as. a substantial shunt or attenuatingQdevice for the primary of output 'transformer 1 6',"-. s0'

far as telephone 'frequen'cies'are concerned. It may alsoact as a shunt or attenuating device for the ringing current-ibut'in any-case it can be made of such wcharacter'that it does not appreciably afiectthe' ringing current flowing through relay 20;} on the other hand the shunt may be of'a character which will not shunt the ringing current but-cause it to follow its former path through the primary winding.

Referring 'inore specifically to the network Z, it isapparent that it may take 9n a large variet of forms. It may, ion-1e:- ample, consi of a simple'shunt selective-for higher frequencies. In Fig. 2, I have shown it as consisting of the impedance elements Z Z and Z5, arranged in a T-formation,

which is adapted for a wide-latitude'of adjustment in regardto impedance characteristics. This latter is desirable for the reasonthe resulting-amplification characteristic is that the introduction of a simple shunt such: given by curves. In some cases it may be whether viewed from the repeater element;

looking towards the output line, or viewed from the output line looking towards the rs-1' peater element. In this Fig. 2'I have; for the purpose of illustration, also shown" a modification in the input circuit. Her again the relays 20 and 24 are connected and operated in the same manner as for Fig. 1. The front contact of the'relay 24; also operand the condenser 27 with the primary of the transformer is highly anti-resonant for the ringing frequency. transmission the presence of the condenser 27 alone would r'endertthe circuit-highly inefficient for voice currents but the pres nee of'theresistance 28; which is given a suitable value, will" maintain a reasonable eflithe transformer 14, However, during th transmission of vo'ice currents thereis, 1n

During ,speech.

' cienc 'y fol 'ispeech currents'which at the same time willbe. less than that given by the cirj ;e,uit O f F Ig QQ IL Thus a fiirther discrimination is givenin favor. of the ringing current.

: Referringto the network introduced in the output circuit, ones ific form which it ma have s shown in 1g. 3, n which Z an Z, are resistance elements, and Z is a .series.resistance and capacity shunted across the line. Byisuitable adjustments of these elements it is possible-to vobtain attenuation without change of thii'iin edance of the cir-' cuit," viewed v in either 'rec'tion. =Fig. 4-.

' shows the amplification characteristic of such a circuit as that of Fig. 3. Curve a gives the am lificationx characteristic for the normal circuit without the network and the introduction of the network issuch asto reduce the amplification to the dotted curve b'.- Thepresence or the anti-resonant circuit in the input circuit, however, alters this substantially at the tin ing fre uency so that thecurve takes-on tl ie modi ed form-indicated by the full .line hump on. the curve 6. The amplitude of the telephone current maynow be restored to substantially its former value by nieans of the potentiometer 17 and a desirable'to remove the condenser from the 1 impedance Z,', which will obviously alter the characteristic for .in-this case the attenuabeselective with respect to ire-- tion will not quencyv Another 'form which the network may 'take on is shownin Fig. 5. It consists of a wave filter of the low pass type now well ing from the introduction ofthe network of t Fig. 5. Theselective nature of the impedance in question is such that the curve I) shows a slight hump at the ringing frequency. However, when the relays and 24 have been operated the efiiciency for-ringing currents has been increased, as indi-' cated by the full line hump on the curve b.

Upon restoring the telephone current to its normal valueby means of the potentiometer 17 there is obtained the characteristic 'ven by curve .0, and thus it is possible to o tain at'the terminal station ringing current of sufiicient' strength tooperate the ringing apparatus.

' Thus; far I have described these networks that thnetwork may be introduced in other parts of-v the circuit; In Fi 7, for example,

I have shown, the networ Z in the secondary of the transformer 16 instead of the primary, the dotted portions of :line indicating that it may be introduc'ed at any desirable place in said line 15. ,Inthis Fig. 7, I have shown the relay mechanism of Figs. 1 and 2 conventionally only at 29, it

'being understood that this relay circuit may be either that of Fig. 1 or Fig. '2. or any such obVl-OUS modifications as might occur to those skilled in the art.

While l have described certain specific.

networks in Figs. 2, 3 and 5, it is to be understood that these are shown for illustrative purposes only and that other forms of networks may be used.

til)

current. and an impedance in the output circuit for further increasing the 'ielative ctiicicncy of amplification of the ringing current coi'npared to the voice frequency cusrent.

2. In a repeater circuit adapted-to amplify voice frequency with high cfiiciency and ringing crrrent with relatively low efficiency, an input and an output circuit therefor, means operative on the input circuit and by the ringing current in the output circuit for increasingthe efiiciency of said repeater for ringing current, and an impedance in the output circuit for further increasing the relative etiiciency of amplificationof the ringing current compared to the voice frequency current. V 3. Ina repeater circuit adapted to amplify voice frequency with high efiiciency and ringing current with relatively lowefiiciency, an input and an output circuit thete- 4 for, a relay controlledby the output ringing current and adapted on operation to.

render the repeater efiicient' for rin mgj current, means in the output circuit for producing a substantial attenuation at the voice frequency currents while prodiicing a negligible attenuation of the ringing current, and means in thef'input circuitfor increasing the gain of the repeater.

4. In a telephone repeater circuit, the method of increasing the relative 'efliciency of amplification of a repeater element for ringing currents which consists in shunting off part-0t the talking current in the output circuit while maintaining substantially constant the apparent-impedance of the output circuit as viewed from said element.

5. In a telephone repeater, circuit, the

method of increasing the efiiciencv of amplification'of a repeater element or ringing' currents which consists in shunting off part of the talking current in the output circuit while maintaining substantially constant the apparent impedance of the output circuit as viewed from saidelement, and in increasing therepeater gain.

\6. In a repeater circuit adapted to amplifylvoice' frequency with high efliciency and ringing current with relatively low eiiiciency, an amplifying repeater having input and output terminals, an input circuit comprisingsaid 'input terminals, an output circuit comprising said output terminals, an incoming line coupledto said input circuit, an outgoing line coupled to said output circuit, means operative on the input circuit for increasing the 'efliciency of said repeater for ringing current, and a network in said output circuit for producing .a substantial attenuation of the voice frequency current while producing a negligible attenuation of' the ringin current, said network being arranged suc that thcimpedance of said outgoing" line, as seen from said output terminals, is substantially unchanged by the presence of said network.

In witness whereof, I hereunto subscribe my name this 15th day of December A. D,

7 CHARLES A. ROBINSON. Witness: 7 y

IVILLIAM A. Knzurnn. 

